Power scaling of high average power fiber sources tends to be limited by pump powers launched into a gain fiber of the fiber source and by the onset of nonlinear optical processes in the fiber. Addressing these limitations often requires balancing conflicting design goals resulting in compromises that negatively impact system performance with regard to total output power, beam quality, wall-plug efficiency, reliability, cost, complexity, and/or manufacturability. The power scaling problems tend to be particularly acute for sources capable of producing single-mode output beams, which are highly desirable for a variety of applications, as output beam powers approach about 1 kW and greater.